The present invention relates generally to push pin actuators and, more specifically, to independent, dual push pin actuators.
Internal combustion (IC) engines are heavily used in automotive, power generation, off-highway, and pump applications. Currently, one of the primary goals in IC engine development is to reduce fuel consumption and carbon dioxide (CO2) emissions. Varying intake and/or exhaust valve timing (i.e., when the valve events occur with respect to the rotation of the crank shaft) in IC engines has been found to reduce fuel consumption and CO2 emissions. Typically, a rotational relationship between the cam shaft (which is coupled to the intake and exhaust valves) and the crank shaft in an IC engine can be varied (i.e., advanced or retarded) by a cam phasing system. Alternatively or additionally, a profile of a lobe on the cam shaft can vary in shape to change the lift profiles of the intake and exhaust valves. Cam profile switching systems can be used to alter between one or more cam lift profiles for the intake and/or exhaust valves. For example, the cam profile switching system may include a cam lobe with a profile which results in no valve lift for a cylinder deactivation operating condition.
FIG. 1 shows a prior art cam profile switching system 100. The cam profile switching system 100 includes solenoid actuators 102 and 104 coupled to push pins 106 and 108, respectively. The solenoid actuators 102 and 104 are configured to fire (i.e., actuate or displace) the push pins 106 and 108 into a respective groove 110 and 112 on the cam shaft 114. The grooves 110 and 112 define spiral profiles. As shown in FIG. 1, the actuator 104 is firing the push pin 108 towards the groove 112. As the push pin 108 seats in the groove 112 and the cam shaft 114 is rotated, the push pin 108 shifts the cam shaft 114 thereby shifting to another cam lobe with a different profile. The push pin 108 is retracted into the actuator 104 by the rotation of the cam shaft 114. Similarly, the push pin 106 can be fired by the actuator 102 to shift the cam shaft 114 back to its original position. In other cam profile switching systems, multiple grooves are added to enable the shifting between more than two cam lobes with different profiles.
Some cam profile switching systems combine actuators into a single package with multiple push pins. Combining the actuators into a single package can allow for a smaller overall package, but these systems do not allow for multiple push pins to extend towards the cam shaft and retract away from the cam shaft independently without assistance from the cam shaft. Additionally, performance with multiple actuators can be hindered due to increased friction from inherent side loading between close proximity actuators combined into a single package.